Sustainable Synthesis of CO2-Derived Polycarbonates from the Natural Product, Eugenol: Terpolymerization with Propylene Oxide

Abstract

Recent years have witnessed tremendous efforts by chemists around the globe for synthesizing sustainable polymers from natural product-based building blocks (monomers). This transition is strongly motivated by the continuous accumulation of non-biodegradable oil-based polymers in the ecosystem, along with long-term goals such as economic and exhaustion of these non-renewable feedstocks. Herein, we report the synthesis of novel terpolymers obtained from the catalytic coupling of renewable eugenol epoxide (EuO), propylene oxide (PO), and CO2 using the well-defined binary (salen)CoTFA/PPNTFA (1) catalyst system. The composition of these polycarbonate terpolymers depends on the relative ratios of EuO and PO employed. To understand the mechanistic details during these terpolymerization reactions, Fineman-Ross analysis of these polymerization reactions were performed. This analysis revealed the reactivity ratios for eugenol epoxide (EuO)/PO to be rEuO = 1.95 and rPO = 0.28, respectively, which in turn reflect both the binding constants of the epoxides to the cobalt center as well as the rate constants for the ring-opening process. Further, the effect of CO2 pressure on the terpolymerization reactions was carried out which confirmed that at ambient pressure (0.1 MPa), only cyclic carbonates were obtained. The thermal analysis of these terpolymers reveals a gradual increase in the Tg values with increase in the eugenol epoxide proportion in the terpolymer. We have also employed a one pot, two step protocol for making EuO/PO based block copolymers.